Biofouling, or biological fouling, is the undesirable accumulation of microorganisms, plants, algae, and animals on submerged structures, such as ships' hulls and immersed sensors. Fouling causes huge material and economic costs in maintenance of mariculture, shipping industries, naval vessels, scientific research, and marine water pipelines. Governments and industry expend substantial resources to prevent and control marine biofouling. Coatings for submerged surfaces are formulated with toxic copper compounds or other special chemistry, which impede growth of barnacles, algae, and other such organisms.
U.S. Patent Application Publication No. 2005/0069519 to Osada, et al. describes an anti-adhesion agent for marine organisms comprising a hydrogel. The hydrogel discourages adhesion through a proton concentration of 10−4 mol/L to 5 mol/L derived from an acidic group of a network macromolecule comprising the hydrogel and/or from an acidic substance existing in the gaps in the network macromolecule.
Other work (see Smith, M. J., et al., “Release Studies of Benzalkonium Chloride from Hydrogel in a Freshwater Environment.” J. Environ. Monit. 2003, Vol. 5: 359), describes the use of hydrogel coatings containing the cationic surfactant benzalkonium chloride (BAC) to prevent the development of biofouling for up to 12 weeks in the marine environment. BAC acts as a biocidal agent to prevent growth of organisms on the surface that is exposed to the water. A rapid initial loss of BAC from the hydrogel film was observed. The loss was found to be a combination of diffusive and mass flow, but the period from 12 to 50 hours appeared to fit to diffusion kinetics and a diffusion coefficient of 7.3×10−8 cm2 s−1 (13° C.) was calculated, an order of 10 times greater than that found in marine water. Subsequently the rate of loss of the residual BAC, for which a diffusion coefficient of 5.7×10−10 cm2 s−1 (15° C.) was measured, was too low to prevent the early stages of biofouling.
Katsuyama, et al. (Katsuyama, Y. et al., “Inhibitory Effects of Hydrogels on the Adhesion, Germination, and Development of Zoospores Originating from Laminaria Angustata.” Macromolecular Bioscience 2002, Vol. 2(4): 163) evaluated the various properties of hydrogels in relation to anti-biofouling properties. Specifically, the inhibition of germination and development of zoospores from Laminaria Angustata on various kinds of hydrogels was studied. The effects of the water content of the hydrogel, the electrical nature, the charge density, and the counter-ions of hydrogels on the inhibition of zoospore germination and the development of gametophytes were investigated. The focus of the study was on modulation of the surface charge and roughness of the hydrogels.